2. Summary – what we discussed and learned (accelerator)
G. Sterbini
(starting from a personal perspective to trigger discussions)
5th June 2019

3. Starting considerations
Improving the present performance of the VdM scans is very challenging and call for (even closer) collaboration between experiments and machine in a series of subjects.
Depending of the experiments, among the contributions to the systematic errors possibly related to the machine we have
scan-to-scan variation,
x-y non-factorization,
orbit stability,
beam current-calibration,
beam-beam effect, …
In this context, the present understanding of the luminosity and emittance evolution can be improved by a closer collaboration with the experiment.
e.g., uncertain breakdown from R. Hawkings (ATLAS)
5th June 2019

4. VdM Bunch from Injectors
H. Bartosik
General consensus on improved quality of the beam form the Injector Chain after 2012, but this did not solved the non-factorization.
For Run3, the strategy in the PSB may change due to the improved LINAC4 emittances, but clear commitment in producing the VdM beam during Run3 first year.
5th June 2019

5. https://indico.cern.ch/event/813285/
Optics for the VdM scan
H. Garcia Morales
Difficulties to measure the optics for VdM scan (b*=19/24 m, Q1 k-mod).
In principle an optics with b*=17 m can be easier to measure.
Can a b*=17 m optics be considered for VdM Run3?
5th June 2019

6. Protocol for the VdM scans
Beam displacement sequence controlled by experiment-provided files: pre-programmed scan are less error prone approach!
Clear non-factorization observed from the experiments...
LHCb is performing a 2D scan aiming to relax the hypothesis of the x-y factorization. Can a similar approach be considered in the other experiment?
M. Holstettler
5th June 2019

7. https://indico.cern.ch/event/813285/
VdM BB simulations
The linear approach used until now should be improved  from single particle parameters to distributions.
To find optimal agreement between the COMBI/Balagura results.
Find a parametrization to apply this correction in the VdM scan (complex BB schedule…)
T. Pieloni
5th June 2019

8. https://indico.cern.ch/event/813285/
Effect along the train
Valerie Lang
Patterns with trains emerged: are they related to BB?
5th June 2019

9. Instrument calibration and precision
M. Palm
Important to track and document the performance of the beam instrumentation (legacy data).
Synergy with LHCb for measuring the ghost bunches.
DOROS performance good for the (limited) intensity drop observed during the VdM scan.
5th June 2019

10. Instrument calibration and precision
M. Gasior
Important to track and document the performance of the beam instrumentation.
Synergy with LHCb for measuring the ghost bunches (limit in the BSRL).
DOROS performance very good for the (small) intensity drop observed during the VdM scan.
5th June 2019

11. VdM scan and crossing angle
Currently unused, Q1 BPMs could be made available during VdM scans to quantify any drifts from zero crossing angle.
Same BPM, same cables, same electronics are used to acquire both beams which eliminates many systematics.
from R. Jones
5th June 2019

12. Orbit stability and Corrector Hysteresis
Orbit feedback is off during the VdM.
Orbit drift has to be taken into account during the scan: more automatic approach to monitor the orbit drift?
ATLAS observed hysteresis effect  systematic characterization during Run 3? can leap-frog scan help?
5th June 2019

13. Emittance measurement
O. Karacheban
[Despite the efforts with WS and BSRT] “Emittance from luminosity not self consistent”.
Significant (and appreciated) efforts from CMS in the emittance scans.
Transverse and longitudinal emittance is a very important input for the luminosity model.
I. Efthymiopoulos 
5th June 2019

14. Bunch-by-bunch luminosity
I. Efthymiopoulos 
First results of the bunch-by-bunch fluctuation presented.
It seems the effect is enhanced in 2018 with the BCMS beams, therefore the interest to further understand it as may affect the machine/experiment performance in Run 3 or HL-LHC.
5th June 2019